The present invention relates to a method for fabricating and passivating semiconductor devices and in particular for fabricating passivating layers on semiconductor devices yielding improved electrical properties.
It has been known for a fairly long time that in the case of III-V compound semiconductors a native oxide layer forming on the semiconductor surface during the fabrication process is the reason why the electrical properties of devices made from such semiconductors are not as good as they should be in theory or as is desirable.
For example, as stated in an article by M. Taillepied and S. Goussier in "Appl. Phys. Lett." 48 (15), 1986, pages 978 to 980, the drain current of field-effect transistors fabricated from III-V compound-semiconductor material is not stable. Also, in photodiodes fabricated from such semiconductor material, too high a dark current is measured, which results in an undesirable noise source in optoelectronic applications. Reduction of this dark current is the subject matter of the published European Patent Application 128 724.
Various authors have proposed methods for suppressing the undesired effect of the native oxide layer during the fabrication of III-V compound-semiconductor devices. This is usually done by preventing or at least reducing the formation of the native oxide layer or by selectively removing the native oxide layer prior to the deposition of an insulating or passivating layer.
In a paper by P. Boher et al from the INFOS 1987 conference at Leuven, Mar. 12 through 14, 1987, and subsequently also appeared in print and comes closest to the present invention, the removal of the native oxide layer using a hydrogen plasma is described. However, even though the substrate surface is coated with silicon nitride (Si.sub.3 N.sub.4) immediately after removal of the native oxide layer, formation of a thinner native oxide layer prior to the coating with Si.sub.3 N.sub.4 cannot be prevented.
The last-mentioned method, as expected, results in an improvement in the electrical values of the semiconductor devices, but this improvement still appears to be insufficient.